Roger Ailes wooed the NBCUniversal-owned network's star anchor with a $6 million salary, but both networks face new digital challenges.

News that MariaBartiromo -- dubbed the "Money Honey" after becoming the first woman to report live from the male-dominated New York Stock Exchange floor -- will leave CNBC after 20 years for Fox Business Network once again has ginned up the competition between the top-rated business news network and its 6-year-old would-be rival.

Bartiromo, 46, hosted her final edition of Closing Bell on Nov. 22. She's expected to host a weekday morning show on Fox Business Network in a deal that is likely to include a significant presence on the more highly viewed Fox News Channel, possibly on Sunday mornings. And she landed a fat pay increase; she was pulling in $4 million at CNBC, say sources, and will make $6 million annually at Fox.

Bartiromo is the latest established personality to join the FBN lineup, after Don Imus, Lou Dobbs and John Stossel. But it remains to be seen whether she can bring a discernible number of her CNBC viewers with her.

"She's a big personality; people like watching her," says Derek Baine, senior analyst at SNL Kagan. But he cautions that the business news landscape, like the rest of TV news, has been roiled by the digital revolution, with apps supplanting the stock ticker and viewers increasingly turning to their smartphones instead of TV for market updates. "If the market's really crashing, you want to turn on the TV to see what's happening. Otherwise, you have an app on your phone that feeds you daily tidbits about the market."

Dobbs, for instance, is pulling in a fraction of the audience he did when he was at CNN; for the fourth quarter, FBN's Lou Dobbs Tonight is averaging just 12,000 viewers in the critical 25-to-54 demographic, according to Nielsen. FBN is in more than 70 million homes; CNN and CNBC are in close to 100 million each. FBN is averaging 10,000 demo viewers this year (in the 6 a.m.-6 a.m. Monday-Friday ratings period), compared with CNBC's 42,000. But CNBC chief Mark Hoffman has complained that the Nielsen sample does not measure the network's out-of-home viewing on trading floors and the offices of business and financial institutions. The sample also does not have enough affluent viewers -- the core CNBC watcher -- to get an accurate picture of CNBC's ratings, they say.

Those affluent viewers are why CNBC, despite shedding viewers since the high-water marks of the dot-com bubble and the 2008 financial crisis, still commands some of the highest ad rates in the industry at $10 per CPM (cost per thousand viewers). FBN earns $4 per CPM, according to estimates provided by SNL Kagan. And while CNBC's net ad revenue has fallen from $239 million in 2011 to $213 million this year, that still eclipses the $38 million FBN is expected to generate -- a number that Roger Ailes, who oversees Fox News and FBN, hopes Bartiromo can increase.